Guilty?

The state of Ohio took twenty years to strap Trevor Lloyd Morden to a gurney and pump him full of lethal drugs. In that time he lost five appeals because his victim’s father, William J. Wendover, fought to ensure his daughter’s killer got what he deserved.
Wendover was convinced of Morden’s guilt but the dead man left a letter saying he was innocent and now Wendover has doubts. He has to know the truth and so he looks for a man who can find it for him.
That man is Dean Witton, ex-marine, ex-cop and ex-husband. His divorce left him broke so he bought a store, lives in the back and works as a private investigator. Dean has a friend, Steph. She is blonde and beautiful and she makes it clear that she would not be against deepening the relationship but Dean is wary.
Despite this he agrees to let her help him investigate the twenty year old murder and, as their romance blossoms, they inadvertently uncover something that alarms someone, alarms them enough to make three attempts to kill Dean. Who is it? Of what are they afraid? Does it mean Morden was not guilty?